You are here:

Recommendations for calculating sound speed profiles from field data

Underwater acoustic propagation models rely on accurate environmental inputs in order to provide reliable predictions of transmission loss and reverberation level. One of the most critical environmental parameters in a propagation model is the vertical sound speed profile (SSP). Using a set of 40 conductivity, temperature, and depth (CTD) measurements, three common techniques of deriving SSPs from field-measured data were investigated to determine whether the choice of technique had an effect on modelled transmission loss (TL): direct measurements of the sound velocity profile, SSPs calculated from expendable bathythermograph (XBT) temperature profiles assuming constant salinity, and SSPs calculated from XBT temperature profiles with an estimated salinity profile derived from a nearby expendable sound velocimeter (XSV) profile. Differences in TL results among the different techniques were likely due to the difference in sound speed gradient at the critical depths just above the sound speed minimum. Based on these results, the preferred method for acquiring multiple SSPs would be to use either CTD or XSV profiles. If XBT profiles are used, assuming a constant salinity avoids the introduction of unphysical values for salinity (and thus the density) that frequently results from the current practice of using a ‘nearby’ XSV drop to estimate a salinity profile; alternatively, the estimated salinity profile should be smoothed to remove obvious outliers before using it to calcula